But if neither Marvel nor Fox ever uses the Scarlet Witch and Quicksilver, we'll never get to see two of the best characters on screen. In Wanda's case, she has to be in the top ten Avengers ever. Neither one of them was aligned with the X-Men when the team began (I'm rather confused as to how they've related to them in recent years) so their absence from those films is a small loss.

Wanda is an Avenger first and foremost, however, and she belongs on the team in the films. As for Pietro, Marvel is moving towards an Inhumans movie for their Cosmic Marvel line-up, and he is a member of the royal family so he should appear with them. The Maximoffs joined the Avengers way back in Avengers #16, along with Hawkeye. Wanda stayed with the team for decades. She will always be associated with the team, no matter how badly various writers have abused her in recent years.

Also, amen to this post.
Scarlet Witch and Quicksilver are FAR more important to the Marvel mythos as Avengers as they are to the Brotherhood. The only thing the mutant/Magneto angle does is blocks the MCU from using story arcs like Avengers Disassembled and House of M.